Metal foil connection, honeycomb body, metal foil brazing medium particle fraction for metal foils and method for manufacturing a metal foil connection

ABSTRACT

A metal foil connection of first and second metal foils having a thickness of less than 0.05 mm includes a connecting point in which the metal foils are brazed to one another. The connecting point forms a wedge which is filled with brazing medium. A mass of the brazing medium, and a mass of sections of the metal foils which the brazing medium contacts in the wedge, have a given ratio. A honeycomb body, a brazing medium particle fraction and a method for manufacturing metal foil connections with a thickness of less than 50 micrometers, are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.09/917,555, filed Jul. 27, 2001, now abandoned which was a continuationof copending International Application No. PCT/EP00/00140, filed Jan.11, 2000, which designated the United States and which was not publishedin English.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a metal foil connection of a first anda second metal foil. The first and second metal foils each have athickness of less than 0.05 mm, and are brazed to one another at aconnecting point. The connecting point forms a wedge which is filledwith brazing medium. The invention furthermore relates to a honeycombbody of sheet metal layers. The sheet metal layers are formed from metalfoils which are at least partly structured and have a thickness of lessthan 0.05 mm. The sheet metal layers are at least partly brazed to oneanother. They have one or two respective wedges filled with brazingmedium at the brazed connecting points. The invention also relates to ametal foil-brazing medium particle fraction for manufacturing a brazedconnection, and a method for manufacturing a metal foil connection ofthe first and second metal foils through the use of a metal foil-brazingmedium particle fraction.

Brazing methods and brazed connections, for example for a metallichoneycomb body, are state of the art for sheet metal layers. GermanPatent DE 42 19 145 C1, corresponding to U.S. Pat. No. 5,431,330,disclose immersing a honeycomb body in a fluidized bed of brazingpowder. The pre-prepared honeycomb body forms brazing medium particlesat desired points from a brazing medium particle fraction. The size ofthe brazing medium particles should be between 1 and 200 micrometers,preferably between 38 and 125 micrometers. Particle sizes in the lowerhalf of that range are more frequently desired than in the upper half.Other methods for applying brazing medium are also disclosed in thatdocument. The methods for applying brazing medium belonging to the priorart are used successfully in brazing honeycomb bodies having sheet metallayers which are made of metal sheets with a material thickness of atleast 50 micrometers and more.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a metal foilconnection, a honeycomb body, a metal foil brazing medium particlefraction for metal foils and a method for manufacturing a metal foilconnection, which overcome the hereinafore-mentioned disadvantages ofthe heretofore-known methods and devices of this general type and whichprovide a durable metal foil connection for thin metal foils with athickness of less than 50 micrometers, in particular less than 40micrometers.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a metal foil connection, comprising afirst and a second metal foil having a thickness of less than 0.04 mm.The first and the second metal foils are brazed to one another at aconnecting point forming a wedge. Brazing medium substantially fills thewedge and has a mass ML. The first and the second metal foils havesections contacted by the brazing medium in the wedge. The sectionshaving a mass MF. The mass ML of the brazing medium and the mass MF ofthe sections of the metal foils contacted by the brazing medium in thewedge are in a given ratio MF/ML of between substantially 4 andsubstantially 8.

With the objects of the invention in view, there is also provided ametal foil connection, comprising a first and a second metal foil havinga thickness DF of less than 0.04 mm. The first and the second metalfoils are brazed to one another at a connecting point forming one or twowedges. Brazing medium fills each wedge and has a mass ML in the wedge.The mass ML of the brazing medium in the wedge and the thickness DF ofthe metal foils are in a ratio ML/DF of substantially between 8 g/m and16 g/m.

When attempting to braze thinner metal foils with a material thicknessof less than 50 micrometers, in particular when manufacturing ahoneycomb body, it was determined that cells simply melt away when thehoneycomb body is brought to the brazing temperature. It was alsodetermined that the cells of the honeycomb body were deformed. It isonly when an amount of brazing medium applied per connecting point wasused in accordance with the rule for adjustment described herein-abovewith respect to sheet metal thicknesses used heretofore, that the amountof brazing medium defined thereby, and introduced into the wedge, couldresult on one hand in the metal foil not becoming detached and formationof gaps at the edges being prevented, while on the other hand a durableconnection of the brazing points was created.

If a metal foil which is used for a metal foil connection has a metalfoil thickness DF of between 0.05 mm and 0.03 mm, the mass of brazingmedium ML to be used for the metal foil connection is selected, in anunexpected manner, in an approximately linear dependency with respect tothe metal foil thickness DF. The thinner the metal foil thickness DF,the less the mass of the brazing medium ML to be used. An upper limit aswell as a lower limit for the mass of brazing medium ML which can stillbe used can consequently be determined for some metal foil thicknessesDF, and interpolated or extrapolated for other metal foil thicknesses.If a relationship is established between the mass of the brazing mediumML and the metal foil thickness DF, an upper limit in the extent of theratio of ML/DF=14.6 g/m, with a variation of +5% and −5% has provedadvantageous. A ratio of ML/DF=8.7 g/m, with a variation of +5% and −5%,has proved advantageous as a lower limit for the still useable ratio ofthe mass of brazing medium ML to the metal foil thickness DF. The rangeto be used for a metal foil thickness DF of less than 0.05 mm toapproximately 0.03 mm, can be very accurately determined from these tworelationships, given as the upper limit and lower limit. The bestresults with respect to the durability of the metal foil connection havebeen produced when a ratio of the mass of the brazing medium ML in thewedge compared to the metal foil thickness DF is approximately ML/DF=11g/m, with a variation of +15% and −10%.

When using metal foil thicknesses DF of approximately 0.03 mm or lessfor the metal foil connection, the linear relationship describedhereinabove can also be used in order to obtain satisfactory results.However, in an unexpected manner, it has been shown that with metal foilthicknesses DF of less than 0.03 mm, it is not only a linearrelationship which exists between the amount of brazing medium that canbe used and the metal foil thickness DF. Instead, the gradient of thislinearity changes with respect to a range of the metal foil thickness DFof less than 0.05 mm to approximately 0.03 mm. It flattens out somewhat.Preferably, with metal foil thicknesses DF of approximately, or lessthan, 0.03 mm, an upper limit of the mass of brazing medium ML isselected in dependence upon the metal foil thickness DF along a curvewhich passes through the following points with coordinates (ML/DF; DF):(14.6 g/m; 0.03 mm), (14.8 g/m; 0.025 mm), (16 g/m; 0.02 mm), (27 g/m;0.01 mm). A lower limit with a metal foil thickness DF of approximately,or less than, 0.03 mm for the mass of brazing medium ML to be used, independence on the metal foil thickness DF, is advantageously selectedfrom a curve which passes along the following points with coordinates(ML/DF; DF): (8.6 g/m; 0.03 mm), (9 g/m; 0.025 mm), (9.2 g/m; 0.02 mm),16 g/m; 0.01 mm). Extremely durable metal foil connections with a metalfoil thickness DF of approximately, or less than, 0.03 mm have beenproduced when the mass of brazing medium ML in dependence on the metalfoil thickness DF is selected from a curve which passes through thefollowing points with coordinates (ML/DF; DF): (11 g/m; 0.03 mm), (11.2g/m; 0.025 mm), (12 g/m; 0.02 mm), (20 g/m; 0.01 mm). A variation of +5%and −5% is also applicable for these curves.

A preferred area of application for the metal foil connections describedhereinabove is honeycomb bodies of sheet metal layers.

With the objects of the invention in view, there is additionallyprovided a honeycomb body, comprising sheet metal layers formed of atleast partly structured metal foils having a thickness of less than 0.04mm or less than 0.05 mm. The sheet metal layers are at least partlybrazed to one another at brazed connecting points. The connecting pointseach have a metal foil connection with two of the metal foils formingone or two wedges. Brazing medium substantially fills the wedges and hasa mass ML. The metal foils have sections contacted by the brazing mediumin the wedges. The sections have a mass MF. The mass ML of the brazingmedium and the mass MF of the sections of the metal foils contacted bythe brazing medium in the wedges are in a given ratio MF/ML of betweensubstantially 4 and substantially 8.

With the objects of the invention in view, there is furthermore provideda honeycomb body, comprising sheet metal layers formed of at leastpartly structured metal foils having a thickness DF of less than 0.04 mmor less than 0.05 mm. The sheet metal layers are at least partly brazedto one another at brazed connecting points. The connecting points eachhave a metal foil connection with two of the metal foils forming one ortwo wedges. Brazing medium fills the wedges and has a mass ML in thewedges. The mass ML of the brazing medium in the wedges and thethickness DF of the metal foils are in a ratio ML/DF of substantiallybetween 8 g/m and 16 g/m.

When using the rules for adjustment set out hereinabove for metal foilconnections, it has been shown that the durability of the honeycomb bodywith respect to mechanical stresses was very much higher as compared towhen using amounts of brazing medium which were previously standard.When using the most widely differing metal foil thicknesses, the mostadvantageous amount of brazing medium could be found in a more rapid andsimple manner by taking into account the rule of adjustment between themass of the brazing medium ML and the metal foil thickness DF. However,not only the durability but also the problems of cell burning, celldeformation, destruction of layers and gap formation at the edgesdescribed hereinabove were avoided by observing the rules for adjustmentfor the metal foil connections.

A further procedure for being able to manufacture a durable metal foilconnection is obtained by using a suitable metal foil-brazing mediumparticle fraction.

Therefore, with the objects of the invention in view, there isfurthermore provided a metal foil-brazing medium particle fraction in abrazed connection between first and second metal foils forming a wedge,in particular for manufacturing a brazed connection in a honeycomb bodyformed of metal foil, comprising a particle size between 0.001 mm or0.01 mm and 0.2 mm. A maximum diameter of 0.135 mm and a minimumdiameter of 0.015 mm are provided for a metal foil thickness ofsubstantially 0.05 mm. A maximum diameter of 0.08 mm and a minimumdiameter of 0.02 mm are provided for a metal foil thickness ofsubstantially 0.02 mm. A substantially linear maximum diameter and asubstantially linear minimum diameter are provided for a metal foilthickness between substantially 0.05 mm and substantially 0.02 mm. Amaximum value of a Gaussian distribution in percent is provided for arespective portion of the diameter disposed substantially centrallybetween the maximum and the minimum diameters.

In an unexpected manner, a linear relationship has been found betweenthe maximum diameter and minimum diameter of the brazing mediumparticles of a brazing medium particle fraction for the respective metalfoil thicknesses to be connected. Furthermore, very durable metal foilconnections for metal foil thicknesses DF of approximately, or lessthan, 0.05 mm, in particular 0.03 mm or less, have been obtained, inthat the maximum value of the Gaussian distribution is not displacedtowards a smaller brazing medium particle fraction as the metal foilthicknesses become less, but instead remains disposed in the centerwithin the distribution. An extremely durable metal foil connectionresulted when the bell-shape of the Gaussian distribution was retainedin the center with decreasing metal foil thicknesses, and when it didnot change with metal foil thicknesses which were up to 0.01 mm.

In the case of a maximum diameter of the brazing medium particlefraction, the following rule for adjustment has proved extremelyadvantageous: the maximum diameter of the brazing medium particlefraction results from the following values:

brazing medium particles with a maximum diameter of 0.125 mm andparticularly 0.105 mm, for a thickness of approximately 0.05 mm;

brazing medium particles with a maximum diameter of 0.07 mm andparticularly 0.063 mm, for a thickness of approximately 0.02 mm; and

a maximum diameter of the brazing medium particles, which is produced inan approximately linear manner from the corresponding values for thethickness of the metal foil of 0.05 mm and 0.02 mm, for a thickness ofmetal foil which lies therebetween.

In the case of a minimum diameter of the brazing medium particlefraction, the following rule for adjustment proved extremelyadvantageous: the minimum diameter of the brazing medium particlefraction results from the following values:

brazing medium particles with a minimum diameter of 0.018 mm, inparticular 0.023 mm, for a thickness of approximately 0.05 mm;

brazing medium particles with a minimum diameter of 0.03 mm, inparticular 0.035 mm, for a thickness of approximately 0.02 mm and

a maximum diameter of the brazing medium particles, which is produced inan approximately linear manner from the corresponding values for thethickness of the metal foil of 0.05 mm and 0.02 mm, for a thickness ofmetal foil which lies therebetween.

In the case of a thickness of the metal foil of 0.03 mm or less, it wasdetermined, in an unexpected manner, that the minimum diameter of thebrazing medium particles should not decrease. Rather, the metal foilconnections were particularly durable when the minimum diameter wasapproximately 0.03 mm, in particular 0.035 mm. Brazing medium particleswith a diameter less than that did not increase durability. Rather, adeterioration was frequently determined.

With the objects of the invention in view, there is also provided amethod for manufacturing a metal foil connection of first and secondmetal foils using a metal foil-brazing medium particle fraction, inparticular for a honeycomb body formed of metal foil, which comprisesproviding the first and second metal foils with a thickness of less than0.05 mm; applying glue to the first and second metal foils; subsequentlyplacing the metal foil-brazing medium particle fraction in contact withthe first and second metal foils; and brazing the first and second metalfoils together at a durable connecting point forming one or two wedges.The metal foil-brazing medium particle fraction is provided with aparticle size between 0.001 mm and 0.2 mm; a maximum diameter of 0.135mm and a minimum diameter of 0.015 mm for a metal foil thickness ofsubstantially 0.05 mm; a maximum diameter of 0.08 mm and a minimumdiameter of 0.02 mm for a metal foil thickness of substantially 0.02 mm;a substantially linear maximum diameter and a substantially linearminimum diameter for a metal foil thickness between substantially 0.05mm and substantially 0.02 mm; and a maximum value of a Gaussiandistribution in percent for a respective portion of the diameterdisposed substantially centrally between the maximum and the minimumdiameters.

With the objects of the invention in view, there is additionallyprovided a method for manufacturing a metal foil connection of first andsecond metal foils using metal foil-brazing medium particle fractions.The method comprises providing the first and second metal foils with athickness of at most 0.03 mm and applying glue to the first and secondmetal foils. The first and second metal foils are subsequently contactedwith a first metal foil-brazing medium particle fraction in a firststep. The first and second metal foils are subsequently again contactedwith a metal foil-brazing medium particle fraction in a second step. Thefirst and second metal foils are brazed together at a connecting pointforming wedges.

In an unexpected manner, a two-step method of application of brazingmedium has proved more advantageous with such material thicknesses ofthe metal foil than a single-step application of brazing medium, despitethe high cost. A better durability was obtained, as well as a bettercontrol of the amount of brazing medium being introduced, as compared toa purely single-step application of the metal foil-brazing mediumparticle fraction.

This two-step method is further improved by selecting the first metalfoil-brazing medium particle fraction in such a way that it has agreater maximum and a smaller minimum diameter of the brazing mediumparticles than a metal foil-brazing medium particle fraction used in thesecond step. Advantageously, in the first step, the first metalfoil-brazing medium particle fraction is adjusted as has previously beendescribed hereinabove. The second metal foil-brazing medium particlefraction is again advantageously selected for the second step s in sucha way that the maximum diameter of the brazing medium particles is lessthan 0.07 mm and the minimum diameter of the brazing medium particles isgreater than 0.04 mm. When these rules for adjustment are observed,particularly durable metal foil connections are produced. In particular,with the brazing of a honeycomb body, the metal foil connections wereproduced with an extremely low or no failure rate, directly after thebrazing procedure, as well as in subsequent tests.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a metal foil connection, a honeycomb body, a metal foil brazingmedium particle fraction for metal foils and a method for manufacturinga metal foil connection, it is nevertheless not intended to be limitedto the details shown, since various modifications and structural changesmay be made therein without departing from the spirit of the inventionand within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, diagrammatic, sectional view of a wedge whichis formed from two metal foils;

FIG. 2 is a graph showing a relationship in which an amount of brazingmedium per connecting point of a metal foil connection is dependent upona metal foil thickness being used;

FIG. 3 is a view similar to FIG. 1 showing a wedge filled with astandard brazing medium particle fraction;

FIG. 4 is another view similar to FIGS. 1 and 3 showing a wedge filledwith a modified brazing medium particle fraction;

FIG. 5 is a graph showing a dependency between the brazing mediumparticle fraction being used and the metal foil thickness being used;

FIG. 6 is a graph showing a relationship in which the amount of brazingmedium being used is dependent upon the metal foil thickness;

FIG. 7 is a graph showing a relationship in which the amount of brazingmedium particle fraction being used is dependent upon the metal foilthickness to be used;

FIG. 8 is a table illustrating a relationship of maximum and minimumratios of a mass ML of the brazing medium to a metal foil thickness DF;

FIG. 9 is a graph showing a Gaussian distribution of a diameter of abrazing medium particle fraction; and

FIG. 10 is a graph showing a further relationship in which the amount ofbrazing medium being used is dependent upon the metal foil thickness.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures of the drawings in detail and first,particularly, to FIG. 1 thereof, there is seen a metal foil connection 1of a first metal foil 2 and a second metal foil 3. The metal foils 2, 3are brazed at a connecting point 4. The connecting point 4 forms anangle or wedge 5 in which the first metal foil 2 and the second metalfoil 3 abut one another. Brazing medium 6 is located in the angle orgusset 5. This brazing medium 6 is in the form of a brazing mediumparticle fraction applied onto a first section 7 of the first metal foil2 and a second section 8 of the second metal foil 3. This is possible,for example according to a method disclosed in German Patent DE 42 19145 C1, corresponding to U.S. Pat. No. 5,431,330, which will be verygenerally referred to below as gluing, and according to the disclosurethereof to which reference will be made. However, the brazing medium 6can be applied according to different brazing medium application methodsdescribed in German Patent DE 42 19 145 C1, corresponding to U.S. Pat.No. 5,431,330, which will also be referred to herein. The first metalfoil 2 and the second metal foil 3 each have a metal foil thickness DFof less than 0.05 mm. The surfaces of the two respective metal foils 2,3 can be prepared in advance for better adhesion of the brazing medium6, or can be provided with microstructures.

A mass ML of the brazing medium 6 which is located in the wedge 5 isadjusted in such a way that a ratio of the mass ML to a mass MF of thefirst section 7 of the first metal foil 2 and the second section 8 ofthe second metal foil 3 is approximately constant regardless of whichmetal foil thickness DF has been selected. The mass MF of the sections7, 8 is calculated by addition of the respective individual masses ofthe first section 7 and the second section 8. These in turn result fromrespective metal foil thicknesses DF and a length LA of the sectionwhich is contacted with brazing medium. The length of the actualabutting together of the two metal foils 2, 3 is also brought into thecalculation. This approximately constant ratio is also obtainedapproximately when the first metal foil 2 has a metal foil thickness DFdifferent from that of the second metal foil 3.

FIG. 2 shows a dependency of the brazing medium mass ML of the brazingmedium at a connecting point upon the metal foil thickness DF which isselected. Accordingly, the approximately linear dependency alreadydescribed above results for a metal foil thicknesses of less than 0.05mm. Not only does the ratio MF/ML=constant, but a gradient of ΔML/ΔDF isalso approximately linear for a durable metal foil connection. Thismakes it possible, when selecting different metal foil thicknesses, toalways be able to immediately extrapolate or interpolate the suitablemass of brazing medium ML. In particular, durable metal foil connectionsin honeycomb bodies have resulted from the following pairs of values (DF[micrometers]; ML [10⁻⁴ grams]) as is clearly shown in FIG. 2: (50;5.5), (40; 4.4), (30; 3.3.), (25; 2.8). If the mass of the brazingmedium ML for the metal foil thickness DF described lies within thesevalues, naturally with a corresponding upper and lower variation ofapproximately 10%, depending on the material composition and on thebrazing method, the cell burning and cell deformation otherwiseoccurring with standard application of brazing medium is prevented.

FIG. 3 shows a further metal foil connection 9. A standard brazingmedium particle fraction 10 according to the prior art is applied in thewedge 5. The wedge 5 is completely closed at its edge 11 because of theuse of this standard brazing medium particle fraction 10. This meansthat between the first metal foil 2 and the second metal foil 3 there isa coherent, completely bonded-together accumulation of brazing medium 6which takes on the shape of a wedge between the metal foils 2, 3.Another metal foil connection, as is described below and shown FIG. 4before brazing, differs therefrom.

FIG. 4 shows a different metal foil connection 12 of a first metal foil2 and a second metal foil 3. The brazing medium 6 is applied to thesetwo metal foils 2, 3 in the form of a first layer 13 on the first metalfoil 2 and a second layer 14 on the second metal foil 3. This isperformed by using a modified brazing medium particle fraction which isdifferent from the standard brazing medium particle fraction describedabove in the general description. There is no danger of the brazingmedium diffusing through the metal foils 2, 3 or leading to a splittingof the edges during brazing, in particular when using a honeycomb bodygeometry, because of the lesser metal foil thickness DF, in particularof 0.03 and less, which is at least due to the smaller amount of brazingmedium in the metal foil connection 12 as compared to the metal foilconnection 9 of FIG. 3.

FIG. 5 shows a relationship between the selection of a suitable brazingmedium particle fraction, shown on the Y axis, and the selected metalfoil thickness DF, shown on the X axis. In the case of a metal foilthickness DF of 50 micrometers, a brazing medium particle fraction isused having a smallest brazing medium particle diameter which is largerthan 25 micrometers, and a largest brazing medium particle diameterwhich is less than 106 micrometers. As the metal foil thickness DFdecreases, the brazing medium particle fraction is adjusted in such away that the largest maximum brazing medium particle diameter iscontinuously reduced, and by contrast the smallest possible brazingmedium particle diameter is continuously increased. This produces theresult that, from a certain metal foil thickness DF onwards, onlybrazing medium particle diameters which are larger than the actual metalfoil thickness DF are present. The maximum value of the Gaussiandistribution thus does not tend downwards, towards ever smaller brazingmedium diameters, with decreasing metal foil thicknesses. Rather, itremains in a bell-shape and proceeds only in the edge areas ever morenarrowly towards the maximum value located at the center. Thisrelationship is shown in a somewhat different manner in FIG. 5. Thebrazing medium particle fractions are combined according to a linearequation along the maximum value of the brazing medium particle diameterof the individual brazing medium particle fraction. This rule foradjustment of the brazing medium particle fraction is described belowwith reference to the following drawings.

FIG. 6 shows a rule for adjustment, in order to be able to manufacturedurable metal foil connections with metal foil thicknesses of less than50 micrometers. In particular, it is used when the connections are to bemetal foil connections of honeycomb bodies for exhaust gas catalyticconverters which are subjected to both thermal and mechanical stresses.On one hand, the mass of the brazing medium ML per metal foil connectionis given in grams on the Y axis. This means the mass which should befound in a wedge. On the other hand, the metal foil thickness DF isentered on the X axis. An upper limit O and a lower limit U of the massML are shown in the diagram. Particularly good durability of the metalfoil connection has resulted when the mass of the brazing medium ML forthe respective metal foil thickness DF is selected along a line I. Itmust be noted in this representation that between the metal foilthickness DF of 20 micrometers and 30 micrometers, an extra metal foilthickness DF of 25 micrometers has been introduced. Due to this, thecurve appears more linear, in particular in the range of less than 30micrometers, than it would be without distortion of the X axis. Despitethis, it can be seen from this diagram, that between 30 micrometers and50 micrometers, there is an approximately linear relationship betweenthe mass ML and the metal foil thickness DF. Below 30 micrometers, thegradient of the curve flattens out somewhat. It is furthermore evidentthat the bandwidth of the selectable mass range narrows ever furtherdownwards in the form of a funnel towards lesser metal foil thicknessesDF. An approximately ideal value of the selected mass ML along the curveI thus runs nearer to the lower limit U than to the upper limit O. Inthe case of a more complex body to be brazed such as, for example, ahoneycomb body, the rule for adjustment for the brazing mediumapplication method is thus to proceed as far as possible along idealvalues according to the curve I. However, care must be taken to ensurethat the lower limit is not gone below. Due to the proximity of thecurve I to the lower limit U, this risk is more likely than exceedingthe upper limit O.

FIG. 7 shows a bandwidth of the particle sizes, entered on the Y axis inmicrometers, in dependence upon the selected metal foil thickness DF,entered on the X axis. This diagram shows in an exemplary manner abandwidth which has been found for the application of brazing medium toa honeycomb body. A first curve 15 with solid triangles shows the limitof the minimum particle size to be selected. A second curve 16 shows amaximum particle size to be selected, depending on the metal foilthickness DF. Particularly good metal foil connections have beenselected for honeycomb bodies when the smallest particle diameter of thebrazing medium particle fraction proceeds along a third curve 17 and thelargest particle diameter of the brazing medium particle fractionproceeds along a fourth curve 18. Furthermore, it can be seen from thediagram that the upper and lower limits of the brazing medium particlefraction with respect to the particle size, with decreasing metal foilthicknesses DF, approach one another in a tubular manner. An absolutevalue for the gradient of the second curve 16 and a fourth curve 18 isthus greater than that of the first curve 15 and the third curve 17. Inparticular, from a metal foil thickness DF of 30 micrometers and lessonwards, the absolute gradient of the first curve 15 and the third curve17 tends towards 0.

FIG. 8 shows the relationship of FIG. 6, wherein in this case, the massof the brazing medium ML depending on the metal foil thickness DF isrepresented as a quotient with respect to the metal foil thickness DF.It is evident that the quotient remains approximately constant up to ametal foil thickness DF of 30 micrometers, while at 30 micrometers andless, the quotient ML/DF increases ever further.

FIG. 9 shows a diagrammatic representation of the Gaussian distributionof the brazing medium particle diameter, in dependence upon the metalfoil thickness DF. The brazing medium particle diameter is entered up tothe maximum brazing medium particle diameter on the Y axis. Thepercentage distribution is shown on the X axis. It is evident that onone hand, the maximum of the brazing medium particle diameter isapproximately central in the bandwidth of the brazing medium particlefraction. It is furthermore evident that the bell-shape does not changein principle as the metal foil thickness DF becomes less, to as small adegree as does the percentage distribution of the brazing mediumparticle fraction per se.

FIG. 10 again shows the dependence of the amount of brazing medium usedupon the metal foil thickness, as already shown in FIG. 6. In FIG. 10,however, the distortion of the X axis is removed, since the distributionis regular. The linearity of the lower limit U, upper limit O and idealdevelopment I up to approximately 20 micrometers, and then the bendingsomewhat, is evident from these measured values.

Overall, particularly good durable metal foil connections, in particularin honeycomb bodies, are produced when a metal foil connection with ametal foil-brazing medium particle fraction and/or a method, asdescribed respectively above, was used.

We claim:
 1. A method for manufacturing an exhaust gas body made of thinmetal foil, comprising: a step of forming a honeycomb body in which10˜25 μm thick corrugated metal foil and flat metal foil are joined bybrazed joints using a brazing powder; the brazing powder having aparticle diameter not greater than 4 times the thickness of the metalfoil constituting the honeycomb body.